什么是.Net的异步机制(APM核心:IAsyncResult) - step 3

墨蓝 2022-01-06 05:43 190阅读 0赞

**异步的核心****: IAsyncResult**

**A****synchronous Programming Model**

整个异步调用过程中都是围绕IAsyncResult来进行的,大家可以看看上篇文章的例子,BeginXXX 返回这个对象,EndXXX接收这个对象来结束当前异步对象,下面我们来看看IAsyncResult 接口成员/和实现此接口的AsyncResult类成员(其中有些在上篇中已经涉及到)

IAsyncResult接口

1 ![None.gif][] public interface IAsyncResult  
2 ![ExpandedBlockStart.gif][] \{  
3![ExpandedSubBlockStart.gif][] WaitHandle AsyncWaitHandle \{ get; \} //阻塞一个线程，直到一个或多个同步对象接收到信号  
4![ExpandedSubBlockStart.gif][] Boolean IsCompleted \{ get; \} //判读当前异步是否完成  
5![ExpandedSubBlockStart.gif][] Object AsyncState \{ get; \} //获取额外的参数值,请看上一篇文章的Code 4.3  
6![ExpandedSubBlockStart.gif][] Boolean CompletedSynchronously \{ get; \} //几乎没有使用  
7![ExpandedBlockEnd.gif][] \}

AsyncResult类

1 ![None.gif][] public class AsyncResult : IAsyncResult, IMessageSink  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] //IAsyncResult 的实现  
4![ExpandedSubBlockStart.gif][] public virtual WaitHandle AsyncWaitHandle \{ get; \}  
5![ExpandedSubBlockStart.gif][] public virtual bool IsCompleted \{ get; \}  
6![ExpandedSubBlockStart.gif][] public virtual object AsyncState \{ get; \}  
7![ExpandedSubBlockStart.gif][] public virtual bool CompletedSynchronously \{ get; \}  
8![InBlock.gif][]  
9![InBlock.gif][] // 其他一些重要的属性  
10![ExpandedSubBlockStart.gif][] public bool EndInvokeCalled \{ get; set; \} //检验是否调用了EndInvoke()  
11![ExpandedSubBlockStart.gif][] public virtual object AsyncDelegate \{ get; \} //获取原始的委托对象,可查看上一篇文章中的Code 4.1/4.2/5  
12![ExpandedBlockEnd.gif][] \}

注意:基本上都是只读属性

下面我们来看看异步的执行顺序,并回顾下 IAsyncResult 下各个属性的应用,如果还是不熟悉请看前2篇文章.

Code 1:

![4.1.jpg][]  
图1

我们看到DoAntherJob 比异步YearlySalary快2秒,看代码中(注1)和(注2),两个线程的执行结果

接下来,我们说说AsyncWaitHandle 属性. 他返回WaitHandle对象(System.Threading.WaitHandle), 他有3个重要的方法. WaitOne / WaitAny / WaitAll ,我们先来说下WaitOne,在Code1代码基础上只是增加了下面红色部分.

**1,WaitOne**

Code 1.1

IAsyncResult ar = del.BeginInvoke(100000, 15, 100000, callback, 2000);  
//阻碍当前线程,直到异步调用结束.  
ar.AsyncWaitHandle.WaitOne();  
//开始其他工作.  
DoAntherJob();

![4.1.1.jpg][]  
图1.1

执行输出,对比图1我们可以看到执行的次序不一样了(看时间),调用WaitOne,会阻碍当前线程,直到异步完成,才释放当前的线程, WaitOne 提供了时间的重载版本WaitOne(int millisecondsTimeout)/ WaitOne(TimeSpan timeout);来判断阻碍的时间.无参的版本是无限等待的(直到异步调用结束)

**2,** **WaitAll**

我们在Code1的代码基础上加上Hello的异步调用(使Main提供多个异步调用),注意红色部分.

Code 1.2

1 ![None.gif][] class Program  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] static void Main(string\[\] args)  
4![ExpandedSubBlockStart.gif][] \{  
5![InBlock.gif][] Console.WriteLine("\[(\#\{1\})\{0\}\]:Asynchronous Start", DateTime.Now.ToString(), Thread.CurrentThread.ManagedThreadId);  
6![InBlock.gif][]  
7![InBlock.gif][] AsyncTest test = new AsyncTest();  
8![InBlock.gif][] MyThirdAsyncCode.AsyncTest.SalaryEventHandler del = test.YearlySalary;  
9![InBlock.gif][] MyThirdAsyncCode.AsyncTest.AsyncEventHandler asy = test.Hello;  
10![InBlock.gif][]  
11![InBlock.gif][] IAsyncResult salayAsyc = del.BeginInvoke(100000, 15, 100000, OnSalaryCallback, null);  
12![InBlock.gif][] IAsyncResult helloAsyc = asy.BeginInvoke("Hello Andy", OnHelloCallback, null);  
13![InBlock.gif][] //把所有异步的句柄保存到WaitHandle 对象中  
14![ExpandedSubBlockStart.gif][] WaitHandle\[\] handles = \{ salayAsyc.AsyncWaitHandle, helloAsyc.AsyncWaitHandle \};  
15![InBlock.gif][] //阻碍当前线程,直到所有异步调用结束.  
16![InBlock.gif][] WaitHandle.WaitAll(handles);  
17![InBlock.gif][]  
18![InBlock.gif][] //开始其他工作.  
19![InBlock.gif][] DoAntherJob();  
20![InBlock.gif][] Console.ReadLine(); // 让黑屏等待,不会直接关闭..  
21![ExpandedSubBlockEnd.gif][] \}  
22![InBlock.gif][] static void DoAntherJob()  
23![ExpandedSubBlockStart.gif][] \{  
24![InBlock.gif][] Thread.Sleep(1000);//需要1秒才能完成这个工作,注1  
25![InBlock.gif][] Console.WriteLine("\[(\#\{1\})\{0\}\]:Do Another Job", DateTime.Now.ToString(), Thread.CurrentThread.ManagedThreadId);  
26![ExpandedSubBlockEnd.gif][] \}  
27![InBlock.gif][] static void OnSalaryCallback(IAsyncResult asyncResult)  
28![ExpandedSubBlockStart.gif][] \{  
29![InBlock.gif][] //通过AsyncDelegate 获取原始的委托对象  
30![InBlock.gif][] AsyncResult obj = (AsyncResult)asyncResult;  
31![InBlock.gif][] MyThirdAsyncCode.AsyncTest.SalaryEventHandler del =  
(MyThirdAsyncCode.AsyncTest.SalaryEventHandler)obj.AsyncDelegate;  
32![InBlock.gif][]  
33![InBlock.gif][] if (asyncResult.IsCompleted)// 判读是否已经调用完成  
34![InBlock.gif][] Console.WriteLine("\[(\#\{1\})\{0\}\]:Asynchronous Finished.", DateTime.Now.ToString(), Thread.CurrentThread.ManagedThreadId);  
35![InBlock.gif][]  
36![InBlock.gif][] decimal val = del.EndInvoke(asyncResult);  
37![InBlock.gif][] Console.WriteLine("\[(\#\{2\})\{0\}\]:Output Result:\{1\}", DateTime.Now.ToString(), val, Thread.CurrentThread.ManagedThreadId);  
38![ExpandedSubBlockEnd.gif][] \}  
39![InBlock.gif][]  
40![InBlock.gif][] static void OnHelloCallback(IAsyncResult asyncResult)  
41![ExpandedSubBlockStart.gif][] \{  
42![InBlock.gif][] //通过AsyncDelegate 获取原始的委托对象  
43![InBlock.gif][] AsyncResult obj = (AsyncResult)asyncResult;  
44![InBlock.gif][] MyThirdAsyncCode.AsyncTest.AsyncEventHandler del =  
(MyThirdAsyncCode.AsyncTest.AsyncEventHandler)obj.AsyncDelegate;  
45![InBlock.gif][]  
46![InBlock.gif][] if (asyncResult.IsCompleted)// 判读是否已经调用完成  
47![InBlock.gif][] Console.WriteLine("\[(\#\{1\})\{0\}\]:Asynchronous Finished.", DateTime.Now.ToString(), Thread.CurrentThread.ManagedThreadId);  
48![InBlock.gif][]  
49![InBlock.gif][] string val = del.EndInvoke(asyncResult);  
50![InBlock.gif][] Console.WriteLine("\[(\#\{2\})\{0\}\]:Output Result:\{1\}", DateTime.Now.ToString(), val, Thread.CurrentThread.ManagedThreadId);  
51![ExpandedSubBlockEnd.gif][] \}  
52![ExpandedBlockEnd.gif][] \}  
53 ![None.gif][]  
54 ![None.gif][] public class AsyncTest  
55 ![ExpandedBlockStart.gif][] \{  
56![InBlock.gif][] public delegate decimal SalaryEventHandler(decimal salary, int monthCount, decimal bonus); // 对应YearlySalary方法  
57![InBlock.gif][] public delegate string AsyncEventHandler(string name); // 对应Hello 方法  
58![InBlock.gif][] public string Hello(string name)  
59![ExpandedSubBlockStart.gif][] \{  
60![InBlock.gif][] //模拟耗时/复杂的逻辑计算.等待5秒  
61![InBlock.gif][] Thread.Sleep(5000);  
62![InBlock.gif][] return "Hello:" + name;  
63![ExpandedSubBlockEnd.gif][] \}  
64![InBlock.gif][] public decimal YearlySalary(decimal salary, int monthCount, decimal bonus)  
65![ExpandedSubBlockStart.gif][] \{  
66![InBlock.gif][] //模拟耗时/复杂的逻辑计算.  
67![InBlock.gif][] Thread.Sleep(3000);//等待3秒  
68![InBlock.gif][] return salary \* monthCount + bonus;  
69![ExpandedSubBlockEnd.gif][] \}  
70![ExpandedBlockEnd.gif][] \}

![4.1.2_r.jpg][]  
图1.2

从图1.2中可以看出,WaitAll会阻碍当前线程(主线程\#10),等待所有异步的对象都执行完毕(耗时最长的异步),才释放当前的线程,WaitAll/WaitAny的重载版本和WaitOne一样.

**3, WaitAny**

和WaitAll 基本上是一样的.我们可以使用 WaitAny 来指定某个/某几个委托先等待,修改Code1.2红色部分,使用WaitAny.

Code1.3  
//把salayAsyc异步的句柄保存到WaitHandle 对象中  
WaitHandle\[\] handles = \{ salayAsyc.AsyncWaitHandle \};  
//阻碍当前线程,直到所有异步调用结束.  
WaitHandle.WaitAny(handles);

![4.1.3_r.jpg][]

图1.3

我们阻碍了DoAntherJob(\#10)线程,直到Salary异步调用计算完成.同样我们可以巧用这三个方法来改变我们方法执行的顺序.

**释放资源**

Code2

1 ![None.gif][] static void OnSalaryCallback(IAsyncResult asyncResult)  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] //通过AsyncDelegate 获取原始的委托对象  
4![InBlock.gif][] AsyncResult obj = (AsyncResult)asyncResult;  
5![InBlock.gif][] MyThirdAsyncCode.AsyncTest.SalaryEventHandler del =  
(MyThirdAsyncCode.AsyncTest.SalaryEventHandler)obj.AsyncDelegate;  
6![InBlock.gif][]  
7![InBlock.gif][] decimal val = del.EndInvoke(asyncResult);  
8![InBlock.gif][] asyncResult.AsyncWaitHandle.Close();//显示的释放资源  
9![ExpandedBlockEnd.gif][] \}

当开始调用BeginXXX后,就会创建一个新的AsyncResult对象.这个对象会构造一个WaitHandle句柄(通过AsyncWaitHandle访问),当我们EndXXX后,并不会马上关闭这个句柄,而是等待垃圾收集器来关闭,这时候我们最后在调用EndXXX完成后,显示的关闭这个句柄.

说到这里,我们基本上把异步方法都解释一遍,下面我们来看看重构的异步对象,我们也可以细细体会异步对象的内部执行代码..下面Code3.1/3.2/3.3代码来自Jeffery Richard大师的Power Threading类库,具体可查看[http://msdn.microsoft.com/en-us/magazine/cc163467.aspx][http_msdn.microsoft.com_en-us_magazine_cc163467.aspx]

**重构的异步对象**

1步,构造一个内部无参的AsyncResultNoResult对象,继承IAsyncResult接口(保留原创的注释)

Code3.1

1 ![None.gif][] internal class AsyncResultNoResult : IAsyncResult  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] // Fields set at construction which never change while  
4![InBlock.gif][] // operation is pending  
5![InBlock.gif][] private readonly AsyncCallback m\_AsyncCallback;  
6![InBlock.gif][] private readonly Object m\_AsyncState;  
7![InBlock.gif][]  
8![InBlock.gif][] // Fields set at construction which do change after  
9![InBlock.gif][] // operation completes  
10![InBlock.gif][] private const Int32 c\_StatePending = 0;  
11![InBlock.gif][] private const Int32 c\_StateCompletedSynchronously = 1;  
12![InBlock.gif][] private const Int32 c\_StateCompletedAsynchronously = 2;  
13![InBlock.gif][] private Int32 m\_CompletedState = c\_StatePending;  
14![InBlock.gif][]  
15![InBlock.gif][] // Field that may or may not get set depending on usage  
16![InBlock.gif][] private ManualResetEvent m\_AsyncWaitHandle;  
17![InBlock.gif][]  
18![InBlock.gif][] // Fields set when operation completes  
19![InBlock.gif][] private Exception m\_exception;  
20![InBlock.gif][]  
21![InBlock.gif][] public AsyncResultNoResult(AsyncCallback asyncCallback, Object state)  
22![ExpandedSubBlockStart.gif][] \{  
23![InBlock.gif][] m\_AsyncCallback = asyncCallback;  
24![InBlock.gif][] m\_AsyncState = state;  
25![ExpandedSubBlockEnd.gif][] \}  
26![InBlock.gif][]  
27![InBlock.gif][] public void SetAsCompleted(  
28![InBlock.gif][] Exception exception, Boolean completedSynchronously)  
29![ExpandedSubBlockStart.gif][] \{  
30![InBlock.gif][] // Passing null for exception means no error occurred.  
31![InBlock.gif][] // This is the common case  
32![InBlock.gif][] m\_exception = exception;  
33![InBlock.gif][]  
34![InBlock.gif][] // The m\_CompletedState field MUST be set prior calling the callback  
35![InBlock.gif][] Int32 prevState = Interlocked.Exchange(ref m\_CompletedState,  
36![InBlock.gif][] completedSynchronously ? c\_StateCompletedSynchronously :  
37![InBlock.gif][] c\_StateCompletedAsynchronously);  
38![InBlock.gif][] if (prevState != c\_StatePending)  
39![InBlock.gif][] throw new InvalidOperationException(  
40![InBlock.gif][] "You can set a result only once");  
41![InBlock.gif][]  
42![InBlock.gif][] // If the event exists, set it  
43![InBlock.gif][] if (m\_AsyncWaitHandle != null) m\_AsyncWaitHandle.Set();  
44![InBlock.gif][]  
45![InBlock.gif][] // If a callback method was set, call it  
46![InBlock.gif][] if (m\_AsyncCallback != null) m\_AsyncCallback(this);  
47![ExpandedSubBlockEnd.gif][] \}  
48![InBlock.gif][]  
49![InBlock.gif][] public void EndInvoke()  
50![ExpandedSubBlockStart.gif][] \{  
51![InBlock.gif][] // This method assumes that only 1 thread calls EndInvoke  
52![InBlock.gif][] // for this object  
53![InBlock.gif][] if (!IsCompleted)  
54![ExpandedSubBlockStart.gif][] \{  
55![InBlock.gif][] // If the operation isn't done, wait for it  
56![InBlock.gif][] AsyncWaitHandle.WaitOne();  
57![InBlock.gif][] AsyncWaitHandle.Close();  
58![InBlock.gif][] m\_AsyncWaitHandle = null; // Allow early GC  
59![ExpandedSubBlockEnd.gif][] \}  
60![InBlock.gif][]  
61![InBlock.gif][] // Operation is done: if an exception occured, throw it  
62![InBlock.gif][] if (m\_exception != null) throw m\_exception;  
63![ExpandedSubBlockEnd.gif][] \}  
64![InBlock.gif][]  
65![ContractedSubBlock.gif][] Implementation of IAsyncResult  
115![ExpandedBlockEnd.gif][] \}

2步,继承AsyncResultNoResult对象,并且为他提供返回值和泛型的访问

Code3.2

1 ![None.gif][] internal class AsyncResult < TResult > : AsyncResultNoResult  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] // Field set when operation completes  
4![InBlock.gif][] private TResult m\_result = default(TResult);  
5![InBlock.gif][]  
6![InBlock.gif][] public AsyncResult(AsyncCallback asyncCallback, Object state) :  
7![ExpandedSubBlockStart.gif][] base(asyncCallback, state) \{ \}  
8![InBlock.gif][]  
9![InBlock.gif][] public void SetAsCompleted(TResult result,  
10![InBlock.gif][] Boolean completedSynchronously)  
11![ExpandedSubBlockStart.gif][] \{  
12![InBlock.gif][] // Save the asynchronous operation's result  
13![InBlock.gif][] m\_result = result;  
14![InBlock.gif][]  
15![InBlock.gif][] // Tell the base class that the operation completed  
16![InBlock.gif][] // sucessfully (no exception)  
17![InBlock.gif][] base.SetAsCompleted(null, completedSynchronously);  
18![ExpandedSubBlockEnd.gif][] \}  
19![InBlock.gif][]  
20![InBlock.gif][] new public TResult EndInvoke()  
21![ExpandedSubBlockStart.gif][] \{  
22![InBlock.gif][] base.EndInvoke(); // Wait until operation has completed  
23![InBlock.gif][] return m\_result; // Return the result (if above didn't throw)  
24![ExpandedSubBlockEnd.gif][] \}  
25![ExpandedBlockEnd.gif][] \}

3步,模拟长时间的异步工作

Code3.3

1 ![None.gif][] internal sealed class LongTask  
2 ![ExpandedBlockStart.gif][] \{  
3![InBlock.gif][] private Int32 m\_ms; // Milliseconds;  
4![InBlock.gif][]  
5![InBlock.gif][] public LongTask(Int32 seconds)  
6![ExpandedSubBlockStart.gif][] \{  
7![InBlock.gif][] m\_ms = seconds \* 1000;  
8![ExpandedSubBlockEnd.gif][] \}  
9![InBlock.gif][]  
10![InBlock.gif][] // Synchronous version of time-consuming method  
11![InBlock.gif][] public DateTime DoTask()  
12![ExpandedSubBlockStart.gif][] \{  
13![InBlock.gif][] Thread.Sleep(m\_ms); // Simulate time-consuming task  
14![InBlock.gif][] return DateTime.Now; // Indicate when task completed  
15![ExpandedSubBlockEnd.gif][] \}  
16![InBlock.gif][]  
17![InBlock.gif][] // Asynchronous version of time-consuming method (Begin part)  
18![InBlock.gif][] public IAsyncResult BeginDoTask(AsyncCallback callback, Object state)  
19![ExpandedSubBlockStart.gif][] \{  
20![InBlock.gif][] // Create IAsyncResult object identifying the  
21![InBlock.gif][] // asynchronous operation  
22![InBlock.gif][] AsyncResult<DateTime> ar = new AsyncResult<DateTime>(  
23![InBlock.gif][] callback, state);  
24![InBlock.gif][]  
25![InBlock.gif][] // Use a thread pool thread to perform the operation  
26![InBlock.gif][] ThreadPool.QueueUserWorkItem(DoTaskHelper, ar);  
27![InBlock.gif][]  
28![InBlock.gif][] return ar; // Return the IAsyncResult to the caller  
29![ExpandedSubBlockEnd.gif][] \}  
30![InBlock.gif][]  
31![InBlock.gif][] // Asynchronous version of time-consuming method (End part)  
32![InBlock.gif][] public DateTime EndDoTask(IAsyncResult asyncResult)  
33![ExpandedSubBlockStart.gif][] \{  
34![InBlock.gif][] // We know that the IAsyncResult is really an  
35![InBlock.gif][] // AsyncResult<DateTime> object  
36![InBlock.gif][] AsyncResult<DateTime> ar = (AsyncResult<DateTime>)asyncResult;  
37![InBlock.gif][]  
38![InBlock.gif][] // Wait for operation to complete, then return result or  
39![InBlock.gif][] // throw exception  
40![InBlock.gif][] return ar.EndInvoke();  
41![ExpandedSubBlockEnd.gif][] \}  
42![InBlock.gif][]  
43![InBlock.gif][] // Asynchronous version of time-consuming method (private part  
44![InBlock.gif][] // to set completion result/exception)  
45![InBlock.gif][] private void DoTaskHelper(Object asyncResult)  
46![ExpandedSubBlockStart.gif][] \{  
47![InBlock.gif][] // We know that it's really an AsyncResult<DateTime> object  
48![InBlock.gif][] AsyncResult<DateTime> ar = (AsyncResult<DateTime>)asyncResult;  
49![InBlock.gif][] try  
50![ExpandedSubBlockStart.gif][] \{  
51![InBlock.gif][] // Perform the operation; if sucessful set the result  
52![InBlock.gif][] DateTime dt = DoTask();  
53![InBlock.gif][] ar.SetAsCompleted(dt, false);  
54![ExpandedSubBlockEnd.gif][] \}  
55![InBlock.gif][] catch (Exception e)  
56![ExpandedSubBlockStart.gif][] \{  
57![InBlock.gif][] // If operation fails, set the exception  
58![InBlock.gif][] ar.SetAsCompleted(e, false);  
59![ExpandedSubBlockEnd.gif][] \}  
60![ExpandedSubBlockEnd.gif][] \}  
61![ExpandedBlockEnd.gif][] \}

来自Jeffrey Richter大师更多更详细的异步操作方法, 请查看[http://www.wintellect.com/PowerThreading.aspx,对于一些朋友可能看不懂Code3.1-3.3代码(其实没什么所谓的),因为涉及到过多的线程知识,这里出于让你获得更多的更深层次的(异步)认识为目的,才提供上面代码,在以后的文章会再次探讨.][http_www.wintellect.com_PowerThreading.aspx_Code3.1-3.3_.]

引用自　：[http://www.cnblogs.com/30ErLi/archive/2010/09/19/1830729.html][http_www.cnblogs.com_30ErLi_archive_2010_09_19_1830729.html]

转载于:https://www.cnblogs.com/zhangchenliang/archive/2012/04/11/2443163.html

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[http_www.wintellect.com_PowerThreading.aspx_Code3.1-3.3_.]: http://www.wintellect.com/PowerThreading.aspx,%E5%AF%B9%E4%BA%8E%E4%B8%80%E4%BA%9B%E6%9C%8B%E5%8F%8B%E5%8F%AF%E8%83%BD%E7%9C%8B%E4%B8%8D%E6%87%82Code3.1-3.3%E4%BB%A3%E7%A0%81%28%E5%85%B6%E5%AE%9E%E6%B2%A1%E4%BB%80%E4%B9%88%E6%89%80%E8%B0%93%E7%9A%84%29,%E5%9B%A0%E4%B8%BA%E6%B6%89%E5%8F%8A%E5%88%B0%E8%BF%87%E5%A4%9A%E7%9A%84%E7%BA%BF%E7%A8%8B%E7%9F%A5%E8%AF%86,%E8%BF%99%E9%87%8C%E5%87%BA%E4%BA%8E%E8%AE%A9%E4%BD%A0%E8%8E%B7%E5%BE%97%E6%9B%B4%E5%A4%9A%E7%9A%84%E6%9B%B4%E6%B7%B1%E5%B1%82%E6%AC%A1%E7%9A%84%28%E5%BC%82%E6%AD%A5%29%E8%AE%A4%E8%AF%86%E4%B8%BA%E7%9B%AE%E7%9A%84,%E6%89%8D%E6%8F%90%E4%BE%9B%E4%B8%8A%E9%9D%A2%E4%BB%A3%E7%A0%81,%E5%9C%A8%E4%BB%A5%E5%90%8E%E7%9A%84%E6%96%87%E7%AB%A0%E4%BC%9A%E5%86%8D%E6%AC%A1%E6%8E%A2%E8%AE%A8.
[http_www.cnblogs.com_30ErLi_archive_2010_09_19_1830729.html]: http://www.cnblogs.com/30ErLi/archive/2010/09/19/1830729.html